There is a need for a small diameter, highly portable heat source, for the internal heating of tubes and tube-sleeve assemblies, in heat exchangers, particularly in steam generators.
The need is particularly difficult to fill where the tubes are small in diameter, that is, for example, having a diameter as small as about 0.75 cm. In addition to the small bore size, often such tubes are installed in locations where access is difficult to obtain.
Conventional approaches are not satisfactory. Induction heating has been used on certain tubing, but the coils required for induction heating cannot be formed to the proper size, that is, sufficiently small, for some applications. A quartz lamp has been used as a radiant heat source on larger diameter tubes, but it also either is not available or cannot be made in sufficiently small diameter.
Electrical resistance heating offers one possible solution, but since the ordinary electrical resistance heating element requires a power supply and cables, once again access and size present problems. These problems are magnified because in some cases the desired temperature may be as high as 1500.degree. C. or even higher. Moreover, the heat application often must be highly concentrated, that is, confined to a zone about 1 inch long along the length of the tube. Often, heat generation must be very rapid, such as less than 5 minutes to attain 1000.degree. C. to 1100.degree. C. or higher.